Many applications require drilling or boring into large objects with long, often thick, drill bits to create a bore hole or to retrieve a core sample of the object. As used herein, the term "drill bit" refers to drill bits, augers, hole cutters, boring bits, coring bits, screws and any other substantially cylindrical device which penetrates a material through rotational motion. The term "drilling" refers to drilling, boring, coring or otherwise advancing a rotating drill bit into an object.
An example of one such drilling application is in the field of forestry where core samples are taken from trees for analysis purposes. The analysis may involve simple determinations such as tree age, growth rate, and penetration of chemicals, in which case, relatively small diameter cores are adequate, or it may entail more sophisticated evaluations such as wood anatomy, wood properties, and data collection for tree breeding program (specific gravity, fiber length and angle, etc.), in which case, larger cores, typically 12 mm (1/2"), are required.
Manual tools for extracting core samples of wood are used commonly by foresters and technicians. The conventional coring tool uses a tubular bit with a tapered, external thread machined on a short, leading section of the tip which is sharpened with a single, peripheral bevel on the exterior. Coring bits are available in various lengths. Foresters generally use somewhat longer bits than necessary to reach the center of the largest expected trees. A square section machined on the driven end of the bit engages a T-handle. The T-handle provides leverage for a user to rotate the bit. After the hollow, threaded bit is twisted into the tree or wood to be sampled, the core is extracted from the drill bit typically with an extractor.
Manual coring of a tree or lumber using these tools can be an arduous task. For obtaining relatively small diameter cores, typically 5 to 7 mm in diameter, these tools generally can be started manually, simply by leaning into the tree, pushing on the T-handle, and rotating. Dense woods, slightly dull bits, or repetitive corings, however, tax an individual's strength and endurance. Moreover, manual starting of 1/2" diameter core bits requires much greater force, generally exceeding the capability of a man leaning into the tool.
Manufacturers of these core tools have developed a fixture for starting them. It consists of a threaded collar which is strapped snugly to the tree with a web harness. Rotating the collar with a large T-handle forces the bit into the tree until its external male thread engages. The starting fixture is then removed, and the core bit is driven through the tree.
Although these fixtures help in starting larger bits, delivering the required torque to the bit remains a strenuous task. For example, the torque required to core large or dense trees with a 1/2" bit ranges from approximately 50 to approximately 100 lb-ft. with a 2-ft. T-handle. Furthermore, it is often necessary to drill the 1/2" core bits completely through the tree, not just to its center. Even boring a single tree under these conditions can be tremendously fatiguing. Moreover, since there is no support or guide for these relatively thin-walled, 12 to 18" long core bits, it is easy to bend the bit, especially when "leaning" into the bit to deliver the required torque. Aside from damaging it, bending the drill bit also causes misalignment or a divergence from the bit's intended path. This misalignment may cause the bit to miss the center of the tree, resulting in an unbalanced, and possibly crooked, core sample. The continuous, arduous task of coring trees using these manual drills and their limited success therefore has chilled their acceptance and wide-spread use.
Several attempts have been made to mechanize the collection of core samples, especially larger diameter cores, using either electrical or hydraulic power tools. These attempts, however, have been met with limited success. Heavy duty electric drills tend to lack sufficient torque and rotate too fast to be safe. Suitable hydraulic tools are not commercially available, and custom-built hydraulic equipment tends to be complicated, expensive, and heavy. Since tree core samples are usually obtained in remote areas, a suitable coring device should be simple to operate, reliable and easily transported. Complicated, heavy equipment which requires maintenance and is prone to failure is clearly not acceptable. Therefore, a need exists for a convenient boring or drilling system that can deliver high torque and initiate boring while maintaining drill bit alignment.
In addition to being labor intensive and generally inconvenient, conventional boring systems lack the means to extract a bit if it becomes lodged in the object being drilled. In the field of forestry, for example, it is common for boring bits to become lodged in trees such that they cannot be backed out or driven forward. This situation arises for example when the bit encounters a hollow pocket or decay wherein the threads of the bit have no bite.
Since the bits used to bore trees cost upwards of $600, there is an economic incentive to extract these bits when they become lodged. To this end, bits are often extricated by falling and splitting the tree. Rivaling the cost of the bit, however, is the cost of the tree. Consequently, when a bit becomes lodged in a tree the decision becomes whether to sacrifice the bit or sacrifice the tree. In either case, a significant asset is lost. Therefore, a need exists for extracting a bit that becomes lodged in the object being drilled, particularly trees, without destroying the object in the removal process.
The present invention fulfills the above-mentioned needs among others.